BOSTON, MA (CBS) – The Department of Homeland Security (DHS) will be releasing bacteria into the MBTA tunnels to test the safety of the subway.

The DHS has installed sensors in the MBTA system to detect biological agents and they’ve been testing to see how the air moves.

Now they want to release particles in the tunnels to see how well the sensors work.

The tests will be held at stations in Cambridge and Somerville.

Federal officials say they test the subway sensors by releasing dead bacteria called B-subtilis. They say it is used in food supplements, has been rigorously tested and has no adverse health effects for low exposure in healthy people.